For patients suffering from congestive heart failure (CHF), the synchronized stimulation of the atrium and both the right and left ventricle by an implantable pacemaker or defibrillator, called cardiac resynchronization therapy (CRT), has been shown to improve the prognosis.
For biventricular (BiV) pacing (stimulation of both ventricles of a heart), both right ventricular (RV) and left ventricular (LV) stimulation electrode leads bearing right ventricular and left ventricular stimulation electrodes are used. The LV electrode lead is implanted via the right atrium and coronary sinus into a LV cardiac vein. Often, several positions are available for the implantation site of the LV electrode lead. In order to be beneficial, the final position of the LV stimulation electrode should be optimized for hemodynamic benefit.
Pacing of the right atrium (RA), right ventricle (RV), and the left ventricle (LV) is performed by delivery of stimulation pulses to the respective heart chamber. The stimulation pulses have strength strong enough to be captured by the respective heart chamber and cause an excitation of the heart chamber's myocardium. Causing an excitation of a heart chamber that leads to contraction of said heart chamber by means of an electric stimulation pulse is called pacing the heart chamber.
Thus stimulated contractions of a heart chamber, called “pace events,” and natural contractions of a heart chamber, called “intrinsic events,” may occur. In a healthy heart, the natural rhythm or rate of intrinsic events is controlled by the sinus node of the heart. Therefore, the natural rhythm of intrinsic events is called “sinus rhythm” or “sinus rate”.
The pacing site of the left ventricular lead for cardiac resynchronization therapy can be optimized by measuring hemodynamic parameters, which increases duration, complexity and costs of the implantation procedure.
Established methods for assessing the efficiency of biventricular pacing are listed in the following. The following methods can be used to optimize the LV lead implant position and also the pacing timing parameters:
a) noninvasive methods or those using the implanted electrodes:                optimize electrical synchrony (ECG)        maximum delay between RV IEGM and LV IEGM during ventricular intrinsic rhythm        maximum plethysmographic pulse pressure during BiV stimulation        maximum SV (Echo, Doppler echo) during BiV stimulation        minimize mitral regurgitation (mitral insufficiency backflow doppler VTI)        optimize mechanical synchrony (tissue doppler)        implanted sensors (peak endocardial acceleration, RV pressure)        
b) invasive measurements:                maximum arterial pulse pressure during BiV stimulation        maximum dp/dtmax of LV pressure during BiV stimulation        minimum LV EDP, LAP, PCWP during BiV stimulation        maximum SV (thermodilution, pulse contour analysis) during BiV stimulation        optimize electrical synchrony (IEGM mapping)        
The methods that reliably assess hemodynamic parameters considerably increase the effort required during implantation, since either additional equipment is needed (e.g. Echo) or invasive measurements are required (e.g. intracardiac catheter).